On Tuesday, Microsoft made group calls free for Skype users who have decided to buy tablets like the Surface instead of a full-fledged Windows PC.

Microsoft made Skype group calls free to “existing platforms” like the Windows PC in April, and has since decided to open that up to tablet users as well. Since adding the free group calling feature, Microsoft saw group calls increase fourfold, the company said.

Microsoft said that most “group” calls actually include just a small number of people, about four or so. “We’ve found that most group calls take place between three or four participants,” the company said. “When building the group video calling experience for modern Windows, we optimized so that the three most talkative people – plus yourself – are visible at the same time.”

Skype group calling supports up to ten people, but only the most talkative people will actually show up in video windows. Microsoft’s competitor, Google, offers its own services, Hangouts, which has always been free for group video chats for up to ten participants.

So far, group video calls are not possible in Windows Phone at all; only group audio calls are supported—probably due to limited screen space. Group instant messaging is also supported.

Skype said in May that it welcomed its two millionth user. Its rival, Google, has never broken out the number of users who use Hangouts.